This MakerBotMars challenge entry design recognises the fundamental constraint in building a Mars base, which is that minimal material can be sent from Earth. I have responded to this constraint by printing the habitats from concrete or a similar material manufactured on Mars. House printing using concrete is a cutting edge technology at present with the first generation small house printers announced for sale recently. Significant earthly technology development is expected over the next decades, but rapid Mars-oriented technology research and development will be needed to be able to locate suitable rock/regolith for concrete manufacture, quarry it, process it to cement, locate, acquire and store water (or maybe some other liquid?) for mixing the cement and controlling the quality for consistent application, then protecting the printed building while the concrete cures. All this presumably needs to be done robotically so that the buildings are in-place when humans arrive, if not totally fitted out. As Mars-based mineral processing develops, more sophisticated buildings will be possible using a greater range of materials. However this entry represents a first non-imported habitat. Three other critical constraints have shaped my design. Because of the extreme cold temperatures and high range of temperatures encountered on Mars, a triple-skinned design has been adopted. Each skin is separated by a void which would be kept at the low ambient atmospheric pressure of Mars, and which would therefore stop convective heat loss from the inner skins, much as a vacuum flask keeps coffee warm. Some low emissivity surface treatment of the facing surfaces of the skins may be needed to reduce radiant heat transfer. This could be installed during printing. Because Mars' atmospheric pressure is only around 1% of Earth's, the habitats will need to be pressurised, reliably and with backup, and one or several airlocks will be needed for people to access the habitat. Each of the 3 skins is designed to e able to hold the pressure required inside the habitat, although in normal operation earth pressure would only be retained in the inner skin, to maximise the insulation effect of the voids. If a leak occurred in the inner skin, this could be detected through rising pressure in the voids, and contained by an outer skin. A series of three air locks are provided, so that at any one time a minimum of 3 doors are closed between unprotected people inside the habitat and the outside low pressure atmosphere. This redundancy allows safety in the unlikely circumstance of simultaneous leakage of 2 doors. Entering the habitat the first air lock would be used for tool storage and gross decontamination. The second lock might provide compressed Martian 'air' for blowing/vacuuming dust off pressure suits. The third lock, at full earth pressure and composition is for suit storage and changing into indoor clothes. The colour coded cutaway image shows the 3 skins, two of the airlocks, inverted pyramid support structures for the inner skins, and bracing between the skins. No windows are provided as they would allow heat loss, would abrade quickly in Mars'Â? dust storms, would not be part of early Mars-based manufacturing capability, and would be an extravagance to carry from earth. On the other hand pressure doors are critical equipment, and would need to be brought from earth and carefully fitted to the airlocks, possibly by the first arrivals. The rounded corners on the skins are designed to make them more resistant to the pressure difference between the inside and outside. It is assumed that the Martian concrete can be made strong enough to contain the pressure - either through careful manufacture, or the addition of a small fibrous component brought from Earth or manufactured on Mars. The habitats are designed to be printed directly onto a pre-smoothed firm base of regolith by a tractor-based robot arm printer which would build up layers at 45 degrees to the horizontal as the tractor moves slowly forward. Habitats could be constructed singly, or fused into chains sharing the one outer skin or maybe two, but retaining separate inner skins, and linked by pressure doors for safety. Joining two or more habitats in this way provides multiple redundancy in case of airlock failure, pressure failure etc. The printing tractor would be fed printing supplies by an independant robotic vehicle transporting cement and water from the processing plants. Constructed entirely in Blender. The shells were constructed using a subdivision surface. Cleaned up non-manifold faces using MeshLab.